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December 30, 2009 > ACWD customers may notice milky-appearing tap water

ACWD customers may notice milky-appearing tap water

Submitted By Frank L. Jahn

If you live in the Tri-City area, you may notice a slightly "milky" appearance to your tap water beginning in late December. This interesting and harmless phenomenon is known as "entrained air." Air entrainment is not caused by leaking pipes or water mains. Because water in the distribution system is under pressure, water will shoot out of a leak, nothing can get sucked in.

"The source of the entrained air will be the water which Alameda County Water District (ACWD) purchases from the San Francisco Public Utilities Commission (SFPUC)," said Walt Wadlow, ACWD General Manager. "The SFPUC is going to switch from the usual Hetch Hetchy supply to source water which will be treated at the Sunol Valley Water Treatment Plant. In the process of changing facilities and sending water through different distribution pipes, air may become dissolved in the water that is delivered to our area. Despite its initially milky appearance, the water will still be perfectly safe to drink."

Because the SFPUC supplies water to many municipalities throughout the Bay Area, Tri-City residents will not be the only ones to experience the entrained air phenomenon. SFPUC officials estimate that the issues creating the entrained air will be resolved by the end of February. According to ACWD water quality personnel, entrained air can cause water to have a milky appearance. The air is dissolved under pressure in the water system, much like carbon dioxide in a bottle of soda. When the tap is turned on, the pressure is released, which allows bubbles to appear, just as removing a cap from a soda bottle causes the soda to fizz. If the glass of water is allowed to stand for a few moments, the air bubbles will rise to the surface and the water will clear.

If your water has a milky appearance, ACWD water quality specialists encourage you to confirm that the phenomenon you are experiencing is entrained air by performing a simple experiment. Rinse out a glass twice and then fill it with cold tap water. After a few moments the water should begin to clear, from the bottom of the glass to the top, as the bubbles rise to the surface. If the water does not clear, you should call the ACWD Water Quality Laboratory at (510) 668-6522.

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